(1) Field of the Invention
The present invention relates to the use of a polymer of ethylene oxide and epihalohydrin as an antistatic additive for polymeric materials consisting of PVC (polyvinyl chloride) and/or other chlorine containing polymers, or polystyrene and/or other styrene containing polymers, including but not limited to polymers of styrene and acrylonitrile, such as ABS (acrylonitrile-butadiene-styrene), or blends of the polymeric materials. In particular, the present invention relates to a semicrystalline antistatic additive containing at least 60% by weight and preferably at least 80% by weight of ethylene oxide with the remainder being epihalohydrin. The present invention also relates to a process for manufacturing an antistatic polymeric material consisting of PVC and/or other chlorine containing polymers, or polystyrene and/or other styrene containing polymers.
(2) Prior Art
The retention and amplification of charges of static electricity on the surface of most plastics, and particularly PVC and ABS, is well known. Plastic materials have a significant tendency to accumulate static electrical charges during processing operations such as milling, calendering, extruding, etc. A sudden discharge of static electrical charges in the form of an electrical arc is not only a fire hazard, but personnel handling the process plastic are exposed to electrical shock. Furthermore, the presence of static electrical charges on sheets of thermal plastic, for example, can cause the sheets to adhere to one another, thus making the separation for further processing more difficult. Moreover, the presence of static electrical charges during manufacturing causes dust to adhere to the molded sheet which results in a coarse surface requiring additional costly polishing operations for forming articles of manufacturing.
To prevent static electrical charges from accumulating during the manufacturing of plastic, during formation of articles of manufacture, and during the useful life of the various articles of manufacture, it is well known to employ various types of antistatic agents by incorporating the agents into the plastic during processing. However, the incorporation of the antistatic agents into various plastics creates many problems. For example, the majority of antistatic agents cannot withstand high temperatures and are destroyed or rendered useless with respect to their antistatic abilities during the hot temperature processing required in conventional molding and fabricating steps for forming articles of manufacture. A majority of the antistatic agents are also either cationic or anionic. They tend to cause the degradation of the resins, particularly PVC and ABS, at hot processing temperatures resulting in discoloration or loss of physical properties. Still other antistatic agents are subject to blooming and frequently leave a coating on the surface of the molds, destroy the surface finish on the articles of manufacture, and reduce the dimensional stability when exposed to heat. In severe cases, the surface of the article of manufacture becomes quite oily and marbleized. The most serious problem of antistatic agents is the loss of original physical properties of the resins they incorporate.
Prior to the present invention, the conventional thinking was that a high molecular weight antistatic agent does not have good antistatic qualities and characteristics as compared to low molecular weight antistatic agents. Moreover, prior thinking was that a high molecular weight polymeric antistatic agent would impair the physical properties of the resins employed therewith, since compatability between two polymeric materials is exceptional rather than common. It is further known that the incorporation of an incompatible material into a resin would cause the loss of physical properties. Exemplary of such prior art is the following patents.
German Offenlegungsschrift No. 1,907,024 having a publication date of Apr. 15, 1971 discloses molding compounds based on vinyl chloride polymers in which a "non-crystalline" elastomeric copolymer of epichlorohydrin and ethylene oxide is employed in PVC, for example, to provide uniform gelling, to provide thermal softening, to provide adequate flow-ability at low temperature, to provide high heat resistance and transparency, to provide mechanical strength and most importantly to improve impact strength. This reference does not recognize the use of copolymers of epihalohydrin and ethylene oxide as antistatic agents. Additionally, the reference states that when less than 30% by weight of epihalohydrin is used, the copolymer is characterized by "poor compatability," and the resulting compound has "insufficient impact resistance".
U.S. Pat. No. 4,588,773 to Federal et al. discloses an antistatic thermoplastic composition wherein the thermoplastic is ABS and the antistatic agent is an epihalohydrin copolymer which includes from about 25% to about 75% by weight epihalohydrin and from about 75% to about 25% alkylene oxide such as ethylene oxide. More preferably, the copolymer includes about 40% to about 60% by weight epichlorohydrin and about 60% to about 40% by weight of alkylene oxide. However, the only copolymer tested in the examples was "a 50/50 copolymer of epihalohydrin and ethylene oxide." A 50/50 copolymer of epihalohydrin and ethylene oxide is amorphous and rubbery. In order for meaningful antistatic properties to exist in the ABS thermoplastic, the patent teaches one to include more than 20% by weight of the epihalohydrin copolymer antistat based upon the combined copolymer and thermoplastic material. In the preferred embodiment, the epichlorohydrin and the alkylene oxide are copolymerized to form an "epichlorohydrin rubber" prior to combination with the ABS resins. It is very difficult to handle the rubbery amorphous) antistatic copolymer as an additive for plastics, particularly in a continuous and automatic process, specifically when weighing and feeding the additive automatically. Furthermore, rubbery crumbs are generally more difficult to disperse into plastics than powders.
A solid, rubbery, essentially wholly amorphous copolymer of epichlorohydrin and ethylene oxide was disclosed in U.S. Pat. No. 3,158,581 to Vandenberg and a process of polymerizing epichlorohydrin and ethylene oxide with an organo-aluminum compound was disclosed in U.S. Pat. No. 3,135,705 to Vandenberg.
A coordination catalyst based on an organoaluminum compound as described in U.S. Pat. Nos. 3,219,591 and 3,642,667 was found to be suitable for the preparation of high molecular weight semicrystalline antistatic copolymers of epichlorohydrin and ethylene oxide in high yield. U.S. Pat. No. 3,219,591 discloses a coordination catalyst system by reacting a trialkylaluminum in the presence of an ether with water and optionally a chelating agent such as acetylacetone (AcAc). U.S. Pat. No. 3,642,667 discloses an improved catalyst by further reacting the above mentioned catalyst with an ether alcohol such as tetrahydrofurfuryl alcohol. It has been found that a chelating agent is essential for the copolymerization of ethylene oxide and epichlorohydrin, although a chelating agent is optional for the homopolymerization of epichlorohydrin.
U.S. Pat. No. 4,304,902 to Landoll discloses a copolymer consisting of 96 to 99.9% by weight of ethylene oxide and 4 to 0.1% by weight of a long chain alkylene oxide. The patent states that the copolymers are important items of commerce useful as detergents and surfactants. This reference does not recognize the use of the copolymer as an antistat for plastics. In particular, the reference does not recognize the copolymer as an antistatic agent for either ABS or PVC.
It is a chief aim of the present invention to provide an antistatic agent for PVC or ABS which has improved antistatic properties over other epihalohydrin copolymer antistats.
It is another aspect of the present invention to provide an antistatic agent comprising a polymer of ethylene oxide and epihalohydrin.
It is a further aim of the present invention to provide an antistat consisting of a copolymer containing greater than 60% by weight and preferably at least 80% by weight of ethylene oxide with a remainder being epihalohydrin.
It is another feature of the present invention to provide a new class of antistatic agents based on semicrystalline polymers of epihalohydrin and ethylene oxide.
It is another aim of the present invention to provide an antistat for polymeric material consisting of PVC and/or other chlorine containing polymers, or for polystyrene and/or other styrene containing polymers, and blends of the polymeric materials.
It is another aim of the present invention to set forth a process of preparing antistatic PVC or ABS by incorporating an ethylene oxide/epihalohydrin polymer.